DE102006036572B4 - Device for superimposed MRI and PET imaging - Google Patents

Abstract

Device (1) for superimposed magnetic resonance tomography and positron emission tomography image display, characterized by a magnetic resonance tomography tube (2) which defines a first field of view along its longitudinal direction (z); a plurality of positron emission tomography detection units (3) arranged opposite one another in pairs around the longitudinal direction (z); the plurality of positron emission tomography detection units (3) defining a second field of view along the longitudinal direction (z); and an arrangement density of the positron emission tomography detection units (3) along the longitudinal direction (z) is optimized such that the second field of view essentially coincides with the first field of view and that more PET detection units (3) in the center of the second field of view in the z direction are omitted as at the edge in the z direction.

Description

The present invention relates to a device for superimposed MRI and PET imaging.

In addition to magnetic resonance imaging (MRI), positron emission tomography (PET) has also become increasingly popular in medical diagnosis in recent years. While MRI is an imaging technique for displaying structures and sectional images inside the body, PET allows visualization and quantification of metabolic activities in vivo.

PET exploits the special features of positron emitters and positron annihilation to quantitatively determine the function of organs or cell areas. The patient is given appropriate radiopharmaceuticals labeled with radionuclides prior to the examination. The radionuclides emit positron upon decay, which interact with an electron after a short distance, resulting in a so-called annihilation. This produces two gamma quanta, which fly apart in the opposite direction (offset by 180 °). The gamma quanta are detected by two opposing PET detector modules within a certain time window (coincidence measurement), whereby the location of the annihilation is determined to a position on the connecting line between these two detector modules.

For detection, the detector module in PET generally has to cover a majority of the gantry arc length. It is divided into detector elements of a few millimeters side length. Each detector element, upon detection of a gamma quantum, generates an event record indicating the time as well as the location of detection, i. H. indicates the corresponding detector element. This information is transmitted to a fast logic and compared. If two events coincide within a maximum time interval, a gamma decay process is assumed on the connecting line between the two associated detector elements. The reconstruction of the PET image is done with a tomography algorithm, i. H. the so-called back projection.

Due to the different information obtained by MRI and PET, superimposed imaging of the two methods is desirable in many cases.

For future systems, it is currently being attempted to combine the imaging methods MRI and PET in one device and to make them usable as simultaneously as possible. Here, as the PET detector module, an avalanche photodiode array (APD photodiode array) with an upstream array of lutetium oxyorthosilicate crystals (LSO crystals) is favored. The 5 schematically shows a perspective view of the structure of a conventional PET detection module according to the prior art. The PET detector module consists of an APD photodiode array 5 with an upstream array of LSO crystals 4 , In the axial direction of the PET detection module is an electrical amplifier circuit (AMP) 6 placed behind the APD photodiode array 5 ,

The PET detector module is a relatively expensive component because of the crystals. For a serial solution, cost-effective approaches would be advantageous.

Another proposal uses a gantry in whose z-direction (longitudinal direction) and circumferential direction an extensive array of APD / LSO detectors is arranged. In a base assembly, an MRI antenna sits within the PET detector and is separated therefrom for mutual interference decoupling by a PET-transmissive, MRI-compatible RF shield.

Typically, an MRI device in the longitudinal direction (z-direction) has an approximately 50 cm long field of view (FOV). A PET system typically has only about 15 cm of field of view (FOV) in the z-direction. To reduce costs for a serial solution, the fact that the MRI examination generally takes significantly longer than the PET data acquisition can be exploited. This makes it possible to detect PET recordings sequentially in time by moving the detector module. If the MRI device has an approximately 50 cm field of view in the z-direction, and the z-direction PET system has an approximately 15 cm field of view, then the PET system would have to be displaced 3 to 4 times around the field of view of the MRI device. The disadvantage of this method is that a mechanical movement is necessary.

The WO 2006/071922 A2 discloses an apparatus for superimposed magnetic resonance tomography and positron emission tomography imaging comprising a magnetic resonance tomography tube and a plurality of paired positron emission tomography detection units disposed in pairs opposite the longitudinal direction of the magnetic resonance tomography tube.

It is the object of the present invention to provide a device for superimposed MRI and PET image display, which on the one hand is inexpensive to manufacture and on the other hand performs no relative movement between the PET system and MRI device.

This object is achieved by the device for superimposed MRI and PET imaging with the features of claim 1. The invention is further developed in the subclaims.

According to the invention, an arrangement density of the PET detection units along the longitudinal direction is optimized so that the second field of view is substantially equal to the first field of view and that more PET detection units (in the center of the second field of view in the z-direction) are used. 3 ) are omitted as at the edge thereof in the z-direction. As a result, the number of PET detection units is advantageously optimized, so that the costs for the PET detection units are reduced and no relative movement between the PET system and the MRI apparatus is required.

With reference to the accompanying drawings, preferred embodiments of the invention will now be described.

In the drawings show

1 Apparatus for overlaid MRI and PET imaging according to the present invention;

2 an arrangement of PET detection units in a device for superimposed MRI and PET imaging according to a first embodiment of the present invention;

3 an arrangement of PET detection units in a device for superimposed MRI and PET imaging according to a second embodiment of the present invention;

4 an arrangement of PET detection units in a device for superimposed MRI and PET imaging according to a third embodiment of the present invention; and

5 schematically a perspective view of the structure of a conventional PET detection module according to the prior art.

Hereinafter, the embodiments of the present invention will be described with reference to the drawings.

The 1 shows a device 1 for superimposed MRI and PET imaging according to the present invention. The device 1 consists of a known MRI tube 2 ,

The MRI tube 2 defines a longitudinal direction z which is orthogonal to the plane of the drawing 1 extends and into the 2 to 4 is shown. The in the 2 to 4 shown y-direction corresponds to a developed circumferential direction of the MRI tube 2 ,

Like this in the 1 shown are coaxial within the MRI tube 2 a plurality of PET detection units arranged in pairs opposite to the longitudinal direction z 3 arranged. The PET detection units 3 preferably consist of an APD photodiode array 5 with an upstream array of LSO crystals 4 and an electrical amplifier circuit (AMP) 6 , However, the invention is not based on the PET detection units 3 with the APD photodiode array 5 and the upstream array of LSO crystals 4 limited, but for detection, as well as other types of photodiodes, crystals and devices can be used.

Image processing for superimposed MRI and PET imaging is performed by a computer 7 ,

Along its longitudinal direction z defines the MRI tube 2 a cylindrical, first field of vision. The multitude of PET detection units 3 defines along the longitudinal direction z a cylindrical, second field of view. According to the invention, the second field of view of the PET detection units is correct 3 essentially with the first field of view of the MRI tube 2 match. This is realized by a corresponding adaptation of the arrangement density of the PET detection units 3 along the longitudinal direction z.

The 2 shows such an arrangement of the PET detection units 3 as well as the structure of the PET detection units 3 according to a first embodiment of the present invention.

Between two adjacent APD photodiode arrays 5 with the respective upstream arrays of LSO crystals 4 There is a gap, creating a checkered pattern.

Here it also becomes clear that the AMP 6 not in the axial direction of the PET detection unit, respectively 3 but in a plane parallel to the longitudinal direction z adjacent to the associated LSO crystals 4 and APD photodiodes 5 , The AMP 6 So they are next to the corresponding LSO crystals 4 and APD photodiodes 5 arranged so that each PET detection unit 3 occupies a smaller space in the radial direction of the gantry.

For example, in the first embodiment, both the first visual field and the second visual field may have a length of 50 cm in the z-direction.

The in the 2 shown arrangement of the PET detection units 3 in the superimposed MRI and PET imaging apparatus according to the first embodiment, the following considerations are based.

The second visual field would be in the classical way by homogeneous occupancy of the entire gantry with PET detection units 3 Due to the so-called 3D technique (eg "Theory and Practice of 3D PET, B. Bendriem, D. Townsend"), a sensitivity distribution results which is significantly higher in the center than at the edge of the second field of view. Furthermore, this increased sensitivity would once again shorten the PET measurement time. However, due to the requirements of MRI, since the patient still has to stay in that position for measurement, this increased sensitivity is not necessary.

The goal is to design the PET system in such a way that it is one to the MRI tube 2 identical field of view is considered (measurement), but also the measuring time is identical.

Therefore, it is possible to build the PET system with reduced sensitivity. It is advantageous if the sensitivity is reduced, in particular in the center, since the highest sensitivity is already present here by the above-mentioned 3D technique anyway.

One conceivable option would be to use shorter crystals at the center of the PET system. This would significantly save costs because the crystals are very expensive. Another conceivable possibility would be to omit whole crystals in the center of the PET system and to then recover the missing information through interpolation. One approach is to omit every other crystal. This is not very cost effective, as per PET detection unit 3 nevertheless the costs for the AMP 6 etc. incurred.

It is preferable, at least in the center of the PET system, for every second PET detection unit 3 omit. This leads to a significantly higher cost savings and additionally offers the possibility of the necessary AMP 6 (Preamplifier and line driver) next to the associated PET detection unit 3 to install. This saves space in the radial direction of the gantry, which is extremely expensive in an MRI system. This solution is in the 2 shown.

The 3 shows another arrangement of PET detection units 3 in a device for superimposed MRI and PET imaging according to a second embodiment of the present invention.

The second embodiment is modified with respect to the first embodiment in that the PET detection units 3 at the end of the second field of view in the z-direction are each oriented so that the LSO crystal array 4 and the APD photodiode array 5 to the middle of the MRI tube 2 are oriented and the associated AMP 6 to the edge of the MRI tube 2 is oriented.

Advantageously, at the outer edges of the second field of view in the z-direction in each case a full ring consisting of the LSO crystal arrays 4 and the APD photodiode arrays 5 arranged, whose AMP's 6 sit outside of the second field of view to increase edge sensitivity.

The 4 shows an arrangement of PET detection units 3 in a superimposed MRI and PET imaging apparatus according to the third embodiment of the present invention.

The third embodiment is modified with respect to the second embodiment in that in the center of the second field of view in the z-direction more PET detection units 3 are omitted as at its edge in the z-direction.

For optimization, the system should be simulated and then an optimized assignment should be defined, preferably using a Modulation Transfer Function (MTF).

The first to third embodiments have the following advantages. First, costs are saved due to the reduced number of the PET detection units 3 ,

In addition, radial space in the gantry is saved as the AMP 6 in addition to the associated LSO crystal arrays 4 and APD photodiode arrays 5 is arranged. This also leads to a cheaper MRI system integration.

Another advantage is the fact that the dimensions of the overall system until further notice by the magnet of the MRI tube 2 be specified. The requirements to keep a PET gantry as short and small as possible for reasons of design and claustrophobia are thus eliminated anyway.

Claims (6)

Contraption ( 1 ) for superimposed magnetic resonance tomography and positron emission tomography imaging, characterized by a magnetic resonance imaging tube ( 2 ) defining a first field of view along its longitudinal direction (z); a plurality of positron emission tomography detection units arranged in pairs opposite one another longitudinally (z) 3 ); wherein the plurality of positron emission tomography detection units ( 3 ) defines a second field of view along the longitudinal direction (z); and an arrangement density of the positron emission tomography detection units ( 3 ) along the longitudinal direction (z) is optimized such that the second field of view substantially coincides with the first field of view, and in the center of the second field of view in the z-direction more PET detection units ( 3 ) are omitted as at the edge thereof in the z-direction. Apparatus according to claim 1, wherein the positron emission tomography detection units ( 3 ) each an avalanche photodiode array ( 5 ) with an upstream lutetium oxyorthosilicate crystal array ( 4 ) and an electrical amplifier circuit ( 6 ) exhibit. Device according to one of claims 1 or 2, wherein between two adjacent positron emission tomography detection units ( 3 ) a distance at least corresponding to a positron emission tomography detection unit ( 3 ) is available. Device according to one of claims 2 or 3, wherein in a positron emission tomography detection unit ( 3 ) the electrical amplifier circuit ( 6 ) in a plane which is parallel to the longitudinal direction (z), next to the lutetium oxyorthosilicate crystal array ( 4 ) and / or the avalanche photodiode array ( 5 ) is arranged. Apparatus according to claim 4, wherein the positron emission tomography detection units ( 3 ) at the end of the second field of view in each case in the longitudinal direction (z) are oriented so that the lutetium oxyorthosilicate crystal array ( 4 ) and / or the avalanche photodiode array ( 5 ) to the center of the magnetic resonance imaging tube ( 2 ) and the electrical amplifier circuit ( 6 ) to the edge of the magnetic resonance imaging tube ( 2 ) is oriented. Device according to one of the preceding claims, wherein at least in the center of the device ( 1 ), in particular of the PET system, every other positron emission tomography detection unit ( 3 ) is omitted.

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